Category: Technology

This one has a supply current of 70 mA at 1.5V and a LED current of 25 mA at 3.3V (actually 25 millivolts measured across the 1 ohm [2 resistors] in series with the LED’s green wire). This calculates to an efficiency of 78.6 percent. The frequency is 250 kHz.

The circuit is almost as simple as the conventional Joule Thief; it requires a diode and 680 pF capacitor in addition to the 1k resistor. The end of the feedback winding that was normally connected to positive is instead connected to the 1k and 680 pF as shown in the picture. I used a SS8050 transistor, which is a Fairchild equivalent to the C8050. It can handle up to 1.5 amp collector current.

The circuit will give more LED current for about the same supply current, or the resistor can be increased to 1.5k to give about the same LED current for less supply current. The two current sensing resistors that are in parallel on the lower right are optional and can be removed, and the LED’s green wire connected directly to the heavy negative wire.

I had hoped to drop from using 40 watt incandescent to 2 watt LED bulbs.

That would be a saving of 228 watts in one chandelier and throughout our house the swap would have a total savings of 570 watts. Not a bad idea but the one we bought to test died in less than 2 weeks. It might have only been one week even.

I thought it would be fun to dissect it and see how it failed and maybe how it worked.

What better way to dissect electronics than with a hammer. “I got me’amer” – Photonic Induction.

It hammered apart quite nicely without any damage to the innards.

The pyramid was just a pack for 28 LED’s tightly packed using insulated standoff tubes. I was not sure at first if all the LED’s were in series or if there was some paralleling going on so the voltage could be lower to drive the LED’s.

It was not a complicated circuit. Some filter caps, two resistors, a diode and a SMD bridge rectifier.

Holly crawdads! It still works? I’m thinking the shrink wrap around the PCB was a bit small and it had managed to short the case to the wire feeding the LED’s. I also noticed one leg of the MB6S bridge rectifier IC was not soldered down and it had almost zero copper under the leg so that could have been causing an intermittent as well.

The Fluke says the PCB is putting out ~81V DC.

The AC ripper riding at the 81V DC offset was quite pronounced at 26V PP. But the LED’s didn’t seem to mind and the human eye couldn’t pickup any 120 Hz flashing if it was causing a problem.

I set my power supply to series mode to output my max at 63v DC. That wasn’t enough DC directly across the 28 LED’s to turn them all on so without any further circuit tracing I can tell the LED’s are in series being each white LED needs over 2v to be forward biased.

I must have been real close to turning the pack on with 63v DC because when I jumper across a couple less LED’s the rest of the LED’s came on. A little more probing with the 63v DC source went too far and “I popped’it” – Photonic Induction again 🙂 I sure wish Photonic Induction wouldn’t have pulled off of YouTube. I loved that YouTube channel. The blackened LED’s are the ones I popped with too much voltage. It was fun while it lasted.

I still don’t have a name for the project, it’s hard to talk about it with someone.

Today I’ve finally managed to set up Discovery Board and STM32 on AVT kit, connect them and debug a simple LED-blinking program. I will write about it, probably tomorrow because it was a real pain in the ass so I think it would be useful for future generations.

LM358N

The following schematic shows a simple DEW sensor circuit diagram using LM358N IC. As the humidity around the circuit goes up, the resistance in the DEW sensor increases. When the resistance reaches a pre-specified level, the circuitry displays a warning message, and shuts down the external device

Under normal conditions, resistance of the dew sensor is low (1 kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal. The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit. When humidity exceeds 80 per cent, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This pushes up the output of IC1 to a high level. As a consequence, the LED inside the opto-coupler is energised. At the same time LED1 provides a visual indication. The opto-coupler can be suitably interfaced to any electronic device for switching purpose. Circuit comprising diode D2, resistors R5 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit. This simple arrangement obviates the requirement for a bulky and expensive step-down transformer.

The current flows through the load M – Motor in one direction when S1 and S4 switches are closed and current flows in the other direction when S2 and S3 switches are closed.

The components that realize the switching action are commonly transistors. Two types of transistors, NPN and PNP for BJTs, N-Channel and P-Channel for MOSFETs are needed for the proper biasing where the high side is P-type and the low side is N-type.

In this project, we use MOSFETs because of their high switching speed and low RDS resistance for low heat dissipation. H-Bridge configuration requires both P and N type MOSFETs but since N-type MOSFETs have improved electrical characteristics, using only N-type for four of the transistors will be ideal. IR2110 half bridge MOSFET and IGBT driver IC allows us to do this. By using a boost-up capacitor, it can bias the high side N-type MOSFETs so we get rid of the P-type.

When you expose the silicon die of a transistor to a light source a charge is produced. CircuitsDIY opened up a 2N3055 transistor and did some experimenting. With the help of a magnifying glass he was able to built up a charge of 0.65V and produce 42.2mA of current.

Most photovoltaic cells are made of silicon chip above which there resides a very thin layer of noble metal through which around 1% of photon particles enter the material and activates electron flow. Here I’m showing how to make one simple solar panel using transistor.

The simplest way to drive stepper motor having lower current rating is using ULN2003. The ULN2003 contains seven darlington transistors. The ULN2003 can pass upto 500mA per channel and has an internal voltage drop of about 1V when on. It also contains internal clamp diodes to dissipate voltage spikes when driving inductive loads. The circuit for driving stepper motor using ULN2003 is shown below.

For higher current torque motors, you can use TIP120. The advantage is that the TIP120 can pass more current along with heat sink. The disadvantages are that the more wiring is required and four TIP120 is used to control the motor.

It uses 2 voltage dividers to give 2.0v to D- and 2.8v to D+, which allows smart(er) phones to take a high current. 1A should be allowed with this setup. If you want 500mA maximum, set D+ to 2.0v just as D- is.

Note: The smoothing capacitors have been excluded from this circuit but will be included in the final design. 470uF on the regulator input, 330uF and 100nF on the output of the regulator.

This long winded intro brings me to the subject of this post: RS485.
This is a serial communications specification that uses differential signaling. The awesome thing about this is that it offers many cool things, one of which is improved noise immunity. As the wire contains the same signal twice (once normal, once inverted) When it gets to the other end, and the inverted signal is transformed into a non-inverted signal and combined with the original signal. Any electrical noise that was picked up is then cancelled out due to wave mechanics. Cool, huh?

Standard Arduino boards use FTDI’s FT232RL to interface with computer’s USB port. Since FT232R is just a USB to UART converter, it is possible to build an Arduino compatible USB interface using other USB to UART chips.

Here is the schematics for using CP2102 with ATmega328p (the circuit below is compatible with the Arduino IDE):

if you compare the above circuit with the official Arduino Duemilanove board you will see that the interfacing portions (RXD, TXD and TDR) are virtually identical.

Since CP2102 comes only in QFN-28 packaging, some people might find it slightly harder to deal with than TSSOP. Using the prototyping method I mentioned a few months back though, it is fairly straightforward to use the chip on a standard perf-board nevertheless. No special tools or stencils are needed. The following picture shows the USB to UART converter portion of the Arduino, which can be used to replace the FT232 break out board. I chose to break out the converter so that I could use it in other projects that require serial connections.